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Abstract

Background

Approximately 1/3 of individuals have a high plasma response to dietary cholesterol
(hyper-responders). Although increases in both LDL and HDL cholesterol have been observed,
limited data exist regarding effects of egg consumption on lipoprotein subclasses
and circulating carotenoids.

Methods

29 postmenopausal women (50–68 y) and 13 men (60–80 y) were assigned to either 3 eggs
(EGG, 640 mg cholesterol/d) or an equal volume of cholesterol-free egg substitute
(SUB, 0 mg cholesterol/d) for 30 d. Following a 3 wk wash out, subjects crossed over
to the alternate diet. Individuals with a response to dietary cholesterol > 2.2 mg/dL
for each additional 100 mg of dietary cholesterol were classified as hyper-responders
while hypo-responders were those with a response ≤ to 2.2 mg/dL. Nuclear Magnetic
Resonance (NMR) spectroscopy determined LDL and HDL size & particle concentrations.
Dietary records were used to evaluate carotenoid consumption.

Results

Hyper-responders had higher concentrations of both LDL (LDL-C) and HDL (HDL-C) cholesterol
after EGG. In contrast, the concentrations of plasma LDL-C and HDL-C did not differ
between the EGG and SUB for the hypo-responders. After EGG, hyper-responders had larger
(≥ 21.2 nm) less atherogenic LDL particle (P < 0.001) and larger HDL particle (> 8.8
nm) (P < 0.01), with no significant difference in the total number of LDL or HDL particles.
Regardless of response classification, all individuals had an increase in plasma lutein
(from 32.4 ± 15.2 to 46.4 ± 23.3 ng/L) and zeaxanthin (from 8.8 ± 4.8 to 10.7 ± 5.8
ng/L) during EGG, yet hyper-responders displayed higher concentrations of carotenoids
when compared to hypo-responders

Conclusion

These findings suggest that the increases in LDL-C and HDL-C due to increased egg
consumption in hyper-responders are not related to an increased number of LDL or HDL
particles but, to an increase in the less atherogenic lipoprotein subfractions. Also,
increases in plasma carotenoids after EGG may provide a valuable dietary source for
this population.

Background

In the United States, people are living longer, healthier lives. Dietary requirements
for the elderly must take into account the physiologic changes that occur with aging
as these needs differ from those of younger adults. Nutritional support in the elderly
is often a primary therapy and it has been shown that those that have an adequate
intake of fatty acids and cholesterol as well as a greater intake of vitamins demonstrate
higher intellectual function than those who have a deficient diet [1-3].

The habitual consumption of eggs has been shown to provide many nutritional benefits
such as higher daily intakes of vitamins C, E and B12, in addition to folate [4]. Deficiencies in these vitamins have been associated with increased risk of cancer,
cardiovascular disease and Alzheimer's disease [5-7]. Therefore, the addition of eggs to the diet could actually prevent disease development,
particularly in this age demographic who are at elevated risks for the onset of chronic
diseases. Additionally, current research has shown that eggs supply a significant
amount of the carotenoids lutein and zeaxanthin, which have been linked to the prevention
of age-related macular degeneration [8-11], the most common cause of blindness in those over the age of 60. On average, each
egg yolk contains 292 μg of lutein and 213 μg of zeaxanthin, along with 0.7 mg vitamin
E, 0.5 mcg vitamin B12, and 23.5 mcg folate, all in a highly bioavailable food matrix
[12,13].

Because of the nutrient density of eggs, they are valuable contributors to overall
nutritional balance, but they are also a source of dietary cholesterol. Currently,
the relationship between plasma cholesterol and dietary cholesterol remains unclear.
High serum cholesterol levels have been linked to increased coronary heart disease
(CHD) [14,15] yet the risk of cardiovascular disease in men and women does not increase with increasing
egg consumption [16-18] despite their high cholesterol content. Summarizing 166 cholesterol feeding studies
conducted over 40 years on 3,500 subjects, a 100 mg/d increase in dietary cholesterol
will raise total cholesterol 2.2 mg/dL or about 1% in normal responders [19]. This response relates to a 1.9 mg/dL change in low density lipoprotein (LDL) cholesterol
and a 0.4 mg/dL increase in high density lipoprotein (HDL) cholesterol, utimately
having little effect on the LDL/HDL cholesterol ratio, and minimal impact on CHD risk
[20]. There is a large variation in response however, and hyper-responders are classified
as those whose total cholesterol concentration will increase >2.2 mg/dL, and hypo-responders
are those for whom total cholesterol increases < 2.0 mg/dL, for every 100 mg/d of
dietary cholesterol consumed [21]. This heterogeneity in response confounds the relationship between dietary cholesterol
and plasma cholesterol.

Plasma lipoproteins are comprised of a group of diverse particles with various physiochemical
characteristics that define each subclass. It is the physiochemical characteristics
that determine the degree of atherogenicity of the lipoprotein particle. In clinical
practice, it is the cholesterol concentration carried in lipoproteins that captures
the attention of the physician. This is the premise behind the use of the LDL and
HDL cholesterol concentration ratio as an assessment of CHD risk. However, the evaluation
of size deviation among lipoprotein subclasses has shown that normocholesterolemic
individuals with a higher concentration of the small, dense LDL particle are at increased
risk for coronary heart disease [22-24], despite similar LDL cholesterol concentrations. Similarly, when analyzing the cholesterol
concentration of the HDL particle, the protective effects are often amplified when
there is a higher concentration the larger subclass (HDL2) which is more antiatherogenic than the smaller HDL3 particle [25-28]. It has been documented that a dietary cholesterol challenge does not impact the
LDL/HDL ratio in premenopausal women [29], or in an elderly population [30] comprised of both genders. In addition, traditional gel electrophoretic analysis
of LDL particle size revealed that the larger LDL particle was predominant in hyper-responders
during a dietary cholesterol intervention [31]. It can be surmised then that the cholesterol concentration that each subclass contains
can vary by particle size, number, and density. Traditional lipoprotein cholesterol
measurements, specifically the LDL/HDL ratio, fail to consider the variability in
size distribution. This high degree of variability may therefore lead to inaccurate
assessment of CHD risk.

The Adult Treatment Panel III recently acknowledged that the predominance of small
dense LDL particles (sdLDL) is an emerging cardiovascular risk factor [32,33]. It has been reported that LDL size was the best predictor of coronary artery disease
[34,35] and the increase in cardiovascular risk, attributable to lipid factors, was significantly
modulated by variations in LDL particle size [32,36]. Utilizing nuclear magnetic resonance (NMR) spectroscopy, Blake, et al [37] found that median baseline values of LDL particle concentration were higher and LDL
particle size was lower among women who subsequently experienced a coronary event.
These evaluations suggest that the measurement of LDL cholesterol content alone is
an inadequate marker of CHD risk in the general population. In a cohort of men from
the Quebec Cardiovascular Study, the association between LDL particle size and the
incidence of ischemic heart disease yielded similar results. In this study, multivariate
analysis indicated that sdLDL particles predicted the rate of ischemic heart disease
independent of LDL cholesterol content and other lipid risk factors [38]. This large scale, prospective evidence supports a hypothesis that LDL particle size
is an important characteristic associated with CHD and that including LDL diameter
analysis in CHD risk assessment may increase the accuracy of the evaluation over traditional
lipid values.

Carotenoids and cholesterol share common pathways in absorption and transport in the
plasma compartment as well as response differences. It is this commonality that led
to this study, whose objectives are to evaluate the changes in lipoprotein size, cholesterol
content and carotenoid concentration in an elderly population following egg consumption
and relate those changes to their impact on CHD risk assessment.

Subjects

Recruitment efforts were conducted through the use of local newspapers and brochure
distribution within the surrounding University community. Men were required to be
over the age of 60 while women were expected to be menopausal for at least one year.
Recruitment of male participants was hindered due to the popular use of reductase
inhibitor medication which excluded almost 60% of the male respondents. Ultimately,
forty-two healthy volunteers (13 men and 29 women) were recruited with the exclusion
criteria consisting of 1) allergy to eggs, 2) use of lipid-lowering medication, 3)
history of heart disease, diabetes or kidney problems, 4) total cholesterol values
higher than 240 mg/dL or total triglyceride levels over 300 mg/dL. The subjects were
instructed to continue to consume their regular diet but to abstain from consuming
eggs outside of those provided by the study. The study was conducted in accordance
with the guidelines of the Institutional Review Board at the University of Connecticut.

Experimental protocol

This study utilized a randomized cross-over design where subjects were initially assigned
to an egg (EGG) or egg substitute (SUB) group for 30 days, followed by a three week
washout period. The subjects were then crossed over to the alternate dietary intervention
and continued for 30 days. Those assigned to the EGG group were expected to consume
3 eggs per day (approximately 640 mg dietary cholesterol). Conversely, the SUB group
was given an equal volume of a cholesterol-free, fat-free product almost identical
in color and consistency to the egg product (0 mg dietary cholesterol). Daily amounts
were provided in individual containers and subjects were instructed to return any
uneaten portion at the beginning of the following week. To ensure that diets during
the intervention periods were equivalent and to calculate the amounts of dietary lutein
and zeaxanthin, two seven-day dietary records were collected. Records included two
weekend days and five non-consecutive weekdays. Nutrient intake was evaluated using
Nutritional Data Systems software (NDS-R) Version 5.0, developed by the Nutrition
Coordinating Center, University of Minnesota, Minneapolis, MN, Food and Nutrient Database
29. The variables of weight, waist and hip circumference, smoking and hormone replacement
status were also measured at baseline and at the end of each treatment period to assess
the influence these factors may have had on plasma lipids and lipoprotein characteristics.

Two fasting (12 h) blood draws were scheduled at the end of each intervention period,
on non-consecutive days, 48 hours apart, for each subject. Whole blood was collected
into tubes containing 0.10 mL/100 mL EDTA to determine plasma lipids. Plasma was separated
by centrifugation at 1500 × g for 20 min at 4°C, and placed into vials containing
PMSF (0.05 mL/100 mL), sodium azide (0.01 mL/100 mL) and aprotinin (0.01 mL/100 mL)
and stored at 4°C until analysis. Plasma lipid analysis occurred within one week of
collection.

Classification of hyper- and hyporesponders

As previously described [39], a modest increase in total cholesterol of 0.05 – 0.06 mmol/L (2–2.2 mg/dL) may be
considered a normal response to a 100 mg dietary cholesterol challenge. Therefore,
because the subjects consumed an additional 640 mg/d of dietary cholesterol, those
that had an increase in total cholesterol (TC) of ≥ 0.41 mmol/L (16 mg/dL) were labeled
hyper-responders and those whose fluctuations in TC were ≤ 0.36 mmol/L (14 mg/dL),
were identified as hypo-responders [29,40,41].

Plasma lipids

Since 1989 our laboratory has participated in the Center for Disease Control/National
Heart, Lung and Blood Institute (CDC-NHLBI) lipid standardization program for quality
control and standardization of plasma TC, TG and HDL-C assays. The coefficients of
variance assessed by the standardization program during this study were 0.76–1.2%
for TC, 1.64 – 2.47% for TG and 1.71 – 2.27% for HDL-C. Plasma lipids were determined
by averaging three values obtained from the separate blood draws.

Analysis included enzymatic TC, as described by Allain et al [42] and triglyceride (TG) calculations [43] with kits from Roche Diagnostics that adjust for free glycerol. High density lipoprotein
cholesterol content (HDL-C) was evaluated after the precipitation of apolipoprotein-B
containing particles with a magnesium chloride and dextran sulfate solution [44]. Low density lipoprotein cholesterol content (LDL-C) was determined using the Friedewald
equation [45].

Plasma lutein and Zeaxanthin determinations

Plasma (200 μl) was prepared for HPLC analysis by combining each sample with an internal
standard of 50 μl ethyl-β-apo-8'-carotenoate (Fluka, Ronkonkoma, NY) and 200 μl ethanol
containing butylated hydroxytoluene, similar to the method previously described [46]. Briefly, the sample was extracted three separate times using a hexane carrier containing
butylated hydroxytoluene while centrifugation facilitated the phase separation. The
solvent was removed with a stream of nitrogen and the resulting hexane layers were
reconstituted with 100 μl of 2-propanol and placed into HPLC injection vials. A Waters
HPLC system equipped with a Varian column (100 × 4.6 mm Microsorb-MN 100-3 C-18),
and preceded by an Upchurch C-18 guard column (Upchurch Scientific, Oak Harbor, WA)
was used to analyze the carotenoid content of the plasma. The isocratic mobile phase
contained 80% acetonitrile, 15% dioxane, 2.5% methanol, 2.5% 2-propanol, 0.01% triethylamine,
and 0.01% ammonium acetate. The internal standard and carotenoid content of the plasma
was detected at 450 nm. All solvents were HPLC grade and were filtered and degassed
before use. Standard curves were compiled from HPLC purified lutein and zeaxanthin.

Lipoprotein size determinations

Based on the natural proton NMR profiles of lipoprotein particles, a spectroscopic
alternative to separation-based methodology was utilized to analyze lipoprotein subclasses
[47-49]. This analysis took place at Liposcience, Inc. and will be briefly described here.
An intermediate field (400 MHz) NMR analyzer (Bruker BioSpin Corp, Billerica, MA)
with an automated flow-injection process was used to measure the lipoprotein subclasses
in plasma samples. The deviations to be seen between lipoprotein subclasses are the
result of the diameter of the phospholipid shell of the particle and are not influenced
by apolipoproteins contained within the shell. The amplitude of each particle's signal
is a measure of the concentration of the lipoprotein subclass. NMR simultaneously
quantifies > 30 lipoprotein subclasses that were empirically grouped into 10 smaller
subclasses based on particle diameter. The ten subclasses analyzed in this study were
large VLDL (>60 nm), medium VLDL (35–60 nm), small VLDL (27 – 35 nm), large LDL (21.2
– 23 nm), medium LDL (19.8 – 21.2 nm), small LDL (18 – 19.8 nm), very small LDL (16.8
– 18 nm), large HDL (8.8 – 13 nm), medium HDL (8.2 – 8.8 nm) and small HDL (7.3 –
8.2 nm).

Statistical analysis

Repeated measures analysis of variance (ANOVA) was used to analyze the effects of
egg consumption on plasma lipids, HDL, VLDL, and LDL particle characteristics and
lutein and zeaxanthin concentrations. Each individual's response to diet (egg or substitute)
was considered as the repeated measure with the response classification used as the
between subject factor. P < 0.05 was considered significant. Data are presented as
means ± SDs for the number of subjects in each group. Statistical analysis was conducted
using SPSS v. 12 for Windows (SPSS, Chicago).

Plasma lipid concentrations

Plasma concentrations for the hyper-responders showed significant diet effects on
plasma lipids (Table 1). Total cholesterol, LDL-C and HDL-C were higher after the EGG period compared to
the SUB period for hyper-responders (P < 0.0001) (Table 1). In contrast, total cholesterol, LDL-C or HDL-C were not different between the EGG
and SUB period for hypo-responders. There was no statistical significance to changes
in triglycerides as a result of diet or response effects during this study (Table
1).

Table 1. Plasma concentrations of total cholesterol LDL-C, HDL-C and TG of male and female
hyper- and hypo-responders during the EGG and placebo (SUB) periods1

Lipoprotein particle size

Comparison of the average VLDL, LDL and HDL particle size in hyper- and hypo-responders
revealed statistical significance only for HDL showing a larger HDL particle seen
during the EGG treatment period for both hyper and hypo-responders (Table 2). VLDL and LDL particle size was not affected by diet or response classification.
The changes in HDL size as a result of egg consumption are indicated in Fig. 1. As seen in the figure the majority of the subjects had an increase in HDL particle
size following EGG period, independent of response classification.

Table 2. VLDL, LDL and HDL Particle Sizes of male and female hyper- and hypo-responders during
the EGG and placebo (SUB) periods1.

Figure 1. Changes in HDL particle size as a result in egg consumption. Each bar represents one
subject.

Individual subclass analysis of the concentration of LDL particles showed a significant
increase in the larger LDL particle during the EGG treatment period for hyper-responders
(Table 3). Particle concentration of the large LDL subclass was 674.7 ± 258.4 μmol/L during
the EGG period and 521.1 ± 267.3 μmol/L during the SUB period for hyper-responders
for a diet effect of P < 0.0001. Comparing response classifications, it was noted
that hyper-responders had an increased concentration of the larger LDL particle (674.7
± 258.4 μmol/L for EGG period) than the concentrations in hypo-responders (543.3 ±
252.2 μmol/L for EGG period) demonstrating a significant response effect. The changes
in the large LDL subclass due to egg intake are illustrated in Fig. 2. The diet effect and the response effect in increasing LDL size are clearly depicted
for all subjects.

Table 3. Concentration of total LDL and LDL sub-fractions of male and female hyper- and hypo-responders
during the EGG and placebo (SUB) periods1.

Figure 2. Changes in concentration of the large LDL subclass due to egg consumption and classification
response. Each bar represents one hyper (blue bars) or hypo (yellow bars).

The concentration of HDL particles also showed a significant response effect as hyper-responders
had an increase in the larger HDL particle concentration when compared to hypo-responders
(Table 4). There were no differences seen for hypo-responders in HDL subclass particle sizes
when comparing dietary interventions.

Table 4. Concentration of total HDL and HDL sub-fractions of male and female hyper- and hypo-responders
during the EGG and placebo (SUB) periods1.

Carotenoid analysis

Analysis of the dietary carotenoids, lutein and zeaxanthin, yielded a significant
diet effect as there was an increased consumption of both carotenoids during the EGG
treatment period. Dietary amounts were 4655 ± 1989 μg and 3429 ± 2003 μg for hyper-responders
during the EGG and SUB treatment periods, respectively, while hypo-responders consumed
4857 ± 3048 μg during the EGG period and 2755 ± 1608 μg during the SUB treatment (Table
5)

Table 5. Dietary and plasma concentrations of lutein + zeaxanthin of male and female hypo-
and hyper-responders during the EGG and placebo (SUB) periods

Plasma evaluation of these carotenoids also revealed a diet effect in lutein and zeaxanthin
concentrations as all subjects increased plasma levels during the EGG period (Table
5). Although absolute plasma concentrations for zeaxanthin were lower than lutein,
the response was similar with an increased plasma concentration seen during the EGG
treatment period with significant elevation noted in the hyper-responders for both
carotenoids. A significant correlation between HDL size and plasma lutein (r = 0.361,
P < 0.05) and zeaxanthin (r = 0.321, P < 0.05) was observed for all subjects during
the egg period (Fig. 3) indicating that the higher concentration of plasma carotenoids were related to the
larger HDL following egg intake.

Figure 3. Correlation between large HDL concentrations and plasma lutein for all subjects during
the egg period.

Discussion

While there is little doubt that there exists a continuum of increasing risk for developing
CHD with increasing plasma cholesterol concentrations, there is uncertainty in the
mechanisms that link hypercholesterolemia and atherosclerosis. For any given LDL cholesterol
concentration there is great variability in the clinical expression of the disease.
Patients with heterozygous familial hypercholesterolemia exhibit a wide array of ages
at which they develop CHD and even patients with homozygous familial hypercholesterolemia
may differ by as much as 30 years in the age at which CHD is clinically expressed
[50]. This striking variability implies a complex and multifaceted mechanism between LDL
cholesterol and the development of atherosclerosis. Clearly, the consideration of
plasma cholesterol alone or ratios that consider only the cholesterol content of lipoproteins
are inadequate indicators of CHD risk. Because the cholesterol content of the LDL
subclass varies with particle size and number, and is derived by calculation not direct
measurements, the inherent use of this value in the estimation of CHD risk is fraught
with errors. The expression of multiple distinct LDL subclasses which differ in pathogenic
roles, offers the opportunity to classify the particle based on its phenotype. Previous
studies have suggested that sdLDL are part of a cluster of dyslipidemias, termed the
atherogenic lipoprotein phenotype [51]. Prospective work has also reported that the sdLDL phenotype is a significant predictor
of CVD [34,36,52]. It stands to reason then that an evaluation of particle size and number should be
included in the assessment of CHD risk. In this study, with an elevation of plasma
cholesterol as a result of the dietary intervention in the hyper-responders, the analysis
of not only changes in lipoprotein cholesterol content but also size and number of
lipoprotein subclasses were useful to elucidate the mechanisms behind the changes
seen in TC levels.

While a significant diet effect was seen in TC, LDL and HDL cholesterol for hyper-responders
during the EGG period, it is valuable to note that there was a concomitant increase
in the large LDL particle concentration in this sub-population. Elevated levels of
large LDL are classified as Pattern A and are considered less atherogenic. The smaller
LDL phenotype, Pattern B, is considered more atherogenic. This small, dense LDL phenotype
is recognized as a strong coronary risk factor independent of traditional lipoprotein
cholesterol ratios [53]. If the small, dense LDL particle is considered pro-atherogenic, as documented elsewhere,
then changes in the large LDL particle may be considered less atherogenic in this
population. This implies that the relationship between changes in plasma cholesterol
levels and increases in CHD risk is incomplete and that the modification of the lipoprotein
particle outside of its cholesterol concentration is critical to the understanding
of the mechanism behind elevated TC. By measuring the particle size and number, through
the efficient NMR technology, we can now visualize the metabolic processes that might
occur during a dietary cholesterol challenge and speculate on the mechanisms involved.
Because the LDL cholesterol content increased significantly, it was important to analyze
the subclass of LDL particle that carried the changes in cholesterol concentration.
NMR data indicated that only the larger LDL particle increased during the EGG period
with hyper-responders demonstrating a significantly larger increase than hypo-responders.
A larger, more buoyant LDL particle is hypothesized to have a reduced susceptibility
to both oxidation and endothelial penetration. This suggests that a less atherogenic
LDL particle is responsible for the increase in LDL cholesterol seen in this study.

Similarly, HDL cholesterol content was elevated during the EGG period for hyper-responders.
HDL is considered the 'good' cholesterol and elevations in this lipoprotein are generally
considered antiatherogenic. This too, relates to the functionality of the particle
as the HDL particle serves to remove excess cholesterol from the body and return it
to the liver for excretion. Analyzing the particle size of the major classes of lipoproteins,
this study shows that there was a significant increase in HDL lipoprotein size as
a result of the EGG treatment, where VLDL and LDL showed no significant changes. The
analysis of HDL subclasses demonstrated a significant increase in the large HDL particle
for hyper-responders. This indicates a cardioprotective effect in this population
as the larger HDL particle has been correlated with decreased CHD risk [54]. Hyper-responders are classically defined as individuals who react to dietary cholesterol
with a large increase in plasma cholesterol. The response shown here indicates that
a portion of the increase in TC is associated with an increase in the larger, antiatherogenic
HDL particle and would therefore offset the effects of increases in LDL cholesterol.
We surmise from this that egg consumption will increase the cardioprotective HDL subclasses
as a means of managing the dietary cholesterol and of balancing cholesterol homeostasis
in these elderly subjects.

The lipid content of the yolk provides a highly bioavailable matrix for the absorption
of lutein and zeaxanthin [12]. Because the SUB diet did not contain additional lutein and zeaxanthin, these carotenoids
where found to significantly increase in the plasma as a result of the EGG treatment.
Interestingly, hyper-responders had a larger increase in carotenoid plasma response,
mimicking their elevated cholesterol response. This suggests a common pathway, given
that both cholesterol and these carotenoids where elevated as a result of the administration
of this diet. The chemical characteristics of lutein and zeaxanthin would not allow
incorporation into the hydrophobic core of lipoproteins but instead permit the free
association with the lipoprotein phospholipid shell. It is known that these carotenoids
are carried primarily in the HDL subclass [55-57] and we have shown that the larger HDL is increasing as a result of this intervention.
We suspect that some of the increased carotenoid intake has found its way into the
plasma compartment coincident with the changes to the HDL particle by means of the
reverse cholesterol transport system. Due to the location of lutein and zeaxanthin
on the surface of lipoproteins, it is possible that these carotenoids could exchange
during particle remodeling, while HDL interacts with other lipoproteins in the plasma
compartment. There is tissue specificity with respect to lutein and zeaxanthin concentration
with the macular pigment having the greatest concentration[46]. Because plasma levels of these carotenoids increase following changes in diet and
supplementation, it is proposed that the antioxidant nature of these carotenoids could
serve to decrease the oxidative stress potential found in the plasma compartment and
thereby reduces oxidative damage. This is the hypothesis behind the use of lutein
and zeaxanthin in the prevention of macular degeneration and might also represent
the mechanism by which they could offer cardioprotective effects.

Conclusion

Taken together these findings suggest that (1) LDL particle numbers do not significantly
increase despite an increase in LDL-C with egg consumption; and (2) lipoprotein size
is positively altered by the consumption of three eggs per day in elderly subjects.
The data shown here displays a significant increase in the larger LDL and HDL particles
for hyper-responders, which suggests an antiatherogenic profile. In addition, the
increase in plasma lutein and zeaxanthin following egg consumption may provide a valuable
source of functional carotenoids in the diet for the population. Within the nutritional
community there is a developing appreciation that health derives, not from avoidance
of particular foods, but from an overall pattern of diet, and it has been suggested
that dietary recommendations should shift from one of avoidance to promotion. This
study suggests that egg consumption may be permitted, and perhaps promoted, in a healthy
elderly population to supplement carotenoid intake with minimal reservations concerning
coronary heart disease risk.

Competing interests

Authors received funding from the American Egg Board/Egg Nutrition Center to carry
out these studies.

Authors' contributions

CMG was involved in the acquisition, analysis and interpretation of data in addition
to drafting the manuscript, DMW made significant contributions to the acquisition
and analysis of the data, RMC was involved in interpretation of data and critical
analysis of intellectual content of the manuscript, JHC contributed to the design,
acquisition and interpretation of the data, and MLF was instrumental in the study's
inception, design and approval while providing critical analysis of data interpretation
and manuscript review.

Acknowledgements

This study was supported by a grant from the American Egg Board/Egg Nutrition Center
and a USDA NRI 02-35200-12312 grant to RMC.

"Expert Panel on Detection ETHBCA: Executive Summary of the third report of the national cholesterol education program
(NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol
in adults (Adult Treatment Panel III).